Systems and methods for photoactivating a photosensitizer applied to an eye

ABSTRACT

An antimicrobial treatment system comprises a wearable photoactivation device. The wearable photoactivation device includes a body configured to be positioned on a head of a subject over one or more eyes of the subject. The body includes one or more windows or openings that allow the one or more eyes to see through the body. The body includes one or more photoactivating light sources coupled to the body and configured to direct photoactivating light to the one or more eyes according to illumination parameters. The illumination parameters determine a dose of the photoactivating light that activates, according to photochemical kinetic reactions, a photosensitizer applied to the one or more eyes and generates reactive oxygen species that provide an antimicrobial effect in the one or more eyes, without substantially inducing cross-linking activity that produces biomechanical changes in the one or more eyes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of, and priority to, U.S.Provisional Patent Application No. 62/152,568, filed Apr. 24, 2015, U.S.Provisional Patent Application No. 62/152,533, filed Apr. 24, 2015, andU.S. Provisional Patent Application No. 62/279,951, filed Jan. 18, 2016,the contents of these applications being incorporated entirely herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure pertains to systems and methods for treating aneye, and more particularly, to systems and methods for activating aphotosensitizer applied to an eye during a treatment.

2. Description of Related Art

Bacterial keratitis is an infection of the cornea caused by bacteria,such as Staphylococcus Aureus and Pseudomonas Aeruginosa. Amoebickeratitis is an infection of the cornea caused by amoeba, such asAcanthamoeba. Fungal keratitis is an infection of the cornea caused byfungi. Such eye infections may cause pain, reduced vision, lightsensitivity, and tearing or discharge. If left untreated, these eyeinfections can cause blindness. Superficial keratitis involves theuppermost layers of the cornea, and after healing, usually leaves noscar on the cornea. On the other hand, deep keratitis affects deepercorneal layers, and after healing, may leave a scar that can affectvision depending on where the scar is located. The treatment of theseeye infections may involve the application of an antimicrobial agent tothe infected eyes.

SUMMARY

Some antimicrobial treatments employ photosensitizers to sterilizetissues. In general, when photosensitizers are applied to tissue andexposed to photoactivating illumination, resulting photochemical kineticreactions can produce antimicrobial agents that place microbes in thetissue under stress and induce an apoptotic or necrotic response in themicrobes.

Example antimicrobial treatments may, for instance, employ formulationsincluding various concentrations of riboflavin as a photosensitizer.After a riboflavin formulation is applied to tissue, illumination of thetissue with ultraviolet A (UVA) light in particular results inphotochemical kinetic reactions that provide an antimicrobial effect.

According to an example embodiment, an antimicrobial treatment systemcomprises a wearable photoactivation device. The wearablephotoactivation device includes a body that defines a chamber shaped tobe positioned over and enclose one or more eyes of a subject. The bodyincludes one or more windows that allow the one or more eyes to seethrough the body. The wearable photoactivation device includes one ormore photoactivating light sources coupled to the body and configured todirect photoactivating light to the one or more eyes according toillumination parameters. The illumination parameters determine a dose ofthe photoactivating light that activates, according to photochemicalkinetic reactions, a photosensitizer applied to the one or more eyes andgenerates reactive oxygen species that provide an antimicrobial effectin the one or more eyes. The wearable photoactivation device includes aninlet configured to couple the body to an oxygen source. The chamberreceives oxygen from the oxygen source via the inlet to modify oxygenconditions in the chamber. The activation of the photosensitizer dependson the oxygen conditions.

The wearable photoactivation device may further include one or moreheating elements coupled to the body and configured to generate heat inthe chamber according to temperature parameters. The temperatureparameters modify, according to photochemical kinetic reactions, theactivation of the photosensitizer applied to the one or more eyes andthe generation of reactive oxygen species that provide the antimicrobialeffect in the one or more eyes.

According to another example embodiment, a wearable antimicrobialtreatment device includes a body shaped to be positioned on a head of asubject over one or more eyes. The body includes one or more openingsthat allow the one or more eyes to see through the body. The wearableantimicrobial treatment device includes one or more photoactivatinglight sources coupled to the body and configured to directphotoactivating light to the one or more eyes according to illuminationparameters. The illumination parameters determine a dose of thephotoactivating light that activates, according to photochemical kineticreactions, a photosensitizer applied to the one or more eyes andgenerates reactive oxygen species that provide an antimicrobial effectin the one or more eyes. The wearable antimicrobial treatment deviceincludes a plurality of guide light sources coupled at a plurality ofpositions about the body and configured to direct visible light to theone or more eyes from a plurality of directions. The wearableantimicrobial treatment device includes a controller configured tooperate the guide light sources to alternately direct the visible lightfrom each direction according to a sequence wherein the subject isdirected to look, with the one or more eyes, in each direction accordingto the sequence and different respective areas of the one or more eyesare exposed to the photoactivating light from the one or morephotoactivating light sources.

According to an additional example embodiment, an antimicrobialtreatment system comprises a wearable photoactivation device. Thewearable photoactivation device includes a body configured to bepositioned on a head of a subject over one or more eyes of the subject.The body includes one or more windows or openings that allow the one ormore eyes to see through the body. The body includes one or morephotoactivating light sources coupled to the body and configured todirect photoactivating light to the one or more eyes according toillumination parameters. The illumination parameters determine a dose ofthe photoactivating light that activates, according to photochemicalkinetic reactions, a photosensitizer applied to the one or more eyes andgenerates reactive oxygen species that provide an antimicrobial effectin the one or more eyes, without substantially inducing cross-linkingactivity that produces biomechanical changes in the one or more eyes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a illustrates a view of an example photoactivation device forphotoactivating a photosensitizer in an antimicrobial treatment,according to aspects of the present disclosure.

FIG. 1b illustrates another view of the example photoactivation deviceof FIG. 1 a.

FIG. 2 illustrates a graph of concentration of reactive oxygen species(ROS) generated when various doses of ultraviolet (UV) light are appliedto corneas treated with a transepithelial riboflavin formulation,according to aspects of the present disclosure.

FIG. 3 illustrates, corresponding to FIG. 1, a graph of concentration ofcross-links generated when the various doses of UV light are applied tocorneas treated with the transepithelial riboflavin formulation,according to aspects of the present disclosure.

FIG. 4 illustrates another example photoactivation device forphotoactivating a photosensitizer in an antimicrobial treatment,according to aspects of the present disclosure.

FIG. 5 illustrates an example method for employing the examplephotoactivation device of FIG. 4, according to aspects of the presentdisclosure.

FIG. 6 illustrates a diagram for photochemical kinetic reactionsinvolving riboflavin and UVA light applied during a corneal treatment,according to aspects of the present disclosure.

DESCRIPTION

Some antimicrobial treatments (also known as antimicrobial photodynamictherapies) employ photosensitizers to sterilize tissues. In general,when photosensitizers are applied to tissue and exposed tophotoactivating illumination, resulting photochemical kinetic reactionscan produce antimicrobial agents that place microbes in the tissue understress and induce an apoptotic or necrotic response in the microbes.

Example antimicrobial treatments may, for instance, employ formulationsincluding various concentrations of riboflavin as a photosensitizer.After a riboflavin formulation is applied to tissue, illumination of thetissue with ultraviolet A (UVA) light in particular results inphotochemical kinetic reactions that provide an antimicrobial effect.

In particular, the stroma may be treated with riboflavin, and UVA lightis delivered to the cornea to activate the riboflavin in the stroma.Upon absorbing UVA radiation, riboflavin undergoes a reaction withoxygen in which reactive oxygen species (ROS) and other radicals areproduced. The ROS can provide an antimicrobial effect in the treatedtissue.

FIGS. 1a, b illustrate an example photoactivation device 100 that isconfigured to activate a photosensitizer, such as riboflavin, that hasbeen applied to eye tissue according to an antimicrobial treatment. Thephotoactivation device 100 combines a plurality of features to enhanceor otherwise control photochemical kinetic reactions that produce anantimicrobial effect in the targeted eye tissue. The photoactivationdevice 100 includes a body 102 that defines a substantially closedchamber 103. As shown in FIGS. 1a, b , the photoactivation device 100fits over the eyes of a subject in a manner similar to eye goggles andmay be coupled more securely to the subject's head with a strap, tape,adhesives, and/or the like. The body 102 includes a window 104 formedfrom glass, plastic, etc., that allows the subject see through thephotoactivation device 100. For instance, the window 104 allows theprocedure to be monitored and also allows the subject to read, watchtelevision, or be otherwise occupied during the treatment.

The conditions in the chamber 103 can be controlled and monitored toachieve desired photochemical kinetic reactions and to provide anantimicrobial effect in the targeted eye tissue. The photoactivationdevice 100 includes photoactivating light sources 106 that emit light(e.g., UVA light) to initiate photochemical kinetic reactions with thephotosensitizer that has been applied to the targeted eye tissue. Thephotoactivating light sources 106 may be light emitting diodes (LED's)that can emit selected wavelengths of light, e.g., 365 nm, 450 nm, etc.

The depth and distribution of the antimicrobial effect may be modulatedthrough a timed increase and/or decrease in temperature in the chamber103 enclosing the targeted eye tissue. Correspondingly, thephotoactivation device 100 includes heating elements 108 that generateheat and increase the temperature within the chamber 103. For instance,the heating elements 108 may include LEDs that can emit electromagneticenergy, such as near-infrared (NIR) light, infrared (IR) light, and/ormicrowaves, to generate heat. Alternatively or additionally, the heatingelements 108 may include resistive heating elements or the like.Furthermore, the temperature of the targeted eye tissue may also bedecreased by applying chilled gas, evaporative cooling systems, chilledliquids, etc.

A controller 116 is coupled to the photoactivating light sources 106.The controller 116 can control the photoactivating light sources 106 toapply light with any combination/sequence of pulses or continuous wavehaving any suitable wavelength, power, irradiance, intensity, duration,duty cycle (for pulses), and/or other illumination parameters.

The controller 116 may also be coupled to the heating elements 108 tocontrol the generation of heat. As shown in FIG. 1b , one or moresensors 114 in the photoactivation device 100 may include temperaturesensors (e.g., thermostat, optical sensors, etc.) that monitor thetemperature in the chamber 103 and provide feedback for the operation ofheating elements 108.

The generation of ROS according to the photochemical kinetic reactionsmay be highly dependent on the oxygen conditions (e.g., concentration,pressure, etc.) in the targeted eye tissue or the environment around thetargeted eye tissue. Correspondingly, the photoactivation device 100 canenhance the antimicrobial effect associated with the ROS by controllingthe amount of oxygen available during photoactivation of thephotosensitizer. The photoactivation device 100 can increase the partialpressure of oxygen in the chamber 103 that encloses the targeted eyetissue. For instance, the partial pressure of the oxygen may be achievedthrough the use of hyperoxic addition of oxygen up to 100% and/orthrough hyperbaric pressurization of up to 2 atm.

As shown in FIGS. 1a, b , the photoactivation device 100 includes aninlet 117 that couples the chamber 103 to an oxygen source 118 via atube 120. Thus, the oxygen source 118 delivers oxygen gas (e.g.,humidified oxygen gas) to the chamber 103 to increase the partialpressure of oxygen. The controller 116 may also be coupled to the oxygensource 118 to control the delivery of oxygen gas to achieve the desiredconcentration of oxygen in the chamber 103. The one or more sensors 114may also include oxygen sensors to monitor the concentration of oxygenand provide feedback for the operation of the oxygen source 118.

The treated tissue may be exposed to a sequence of different oxygenconditions to generate different amounts of ROS at different depths inthe treated tissue. For instance, example antimicrobial treatments mayexpose the target tissue to normoxic conditions, followed by hyperoxicconditions, and then followed by hyperbaric conditions.

The oxygen gas in the oxygen source 118 has a temperature that may alsobe controlled by the controller 116. In particular, the oxygen gas maybe kept at a lower temperature that allows the oxygen gas to be used asa cooling agent to control the temperature in the chamber 103. Theoxygen source 118 includes one or more sensors 122 that measure thetemperature of the oxygen gas and provide feedback to manage thetemperature of the oxygen gas.

Accordingly, in combination with the photoactivation device 100, thecontroller 116 can control various aspects of the antimicrobialtreatment applied to the targeted eye tissue and achieve moreoptimal/efficient antimicrobial effects from the photochemical kineticreactions. In particular, the controller 116 can modulate: (i) the lightfrom the photoactivating light sources 106; (ii) the heat generated bythe heating elements 108; (iii) the concentration of oxygen gas in thechamber 103; and/or (iv) the cooling provided by the oxygen gas. Thecontroller 116 can modulate these aspects of the antimicrobial treatmentin any combination and sequence of steps. For example, the controller116 may initially increase the temperature of the treated tissue bygenerating heat with the heating elements 108 and, after a certainperiod of time, may cool the treated tissue by applying cooled oxygengas from the oxygen source 118.

In some embodiments, the window 104 may include a diffuser to allowother external illumination systems to deliver light additionally oralternatively to the treated tissue. Although not shown, aspects of thecontroller 116 and/or the oxygen source 118 may be coupled to orotherwise combined with the photoactivation device 100 in a single unit.

The one or more sensors 114, 122 provide feedback for modulating theseaspects of the antimicrobial treatment. In some cases, additionalmonitoring can be provided by additional systems. For example, afluorescence dosimetry system may be employed to determine thedistribution/uptake of the photosensitizer as well as the consumption ofthe photosensitizer during/after the antimicrobial treatment. An exampleof a fluorescence dosimetry system is described in U.S. Pat. No.9,020,580, filed Jun. 4, 2012 and titled “Systems and Methods forMonitoring Time Based Photo Active Agent Delivery or Photo Active MarkerPresence,” the contents of which are incorporated entirely herein byreference.

The photoactivation device 100 shown in FIGS. 1a, b demonstrates how adevice can combine a variety of the features above to enhance orotherwise control photochemical kinetic reactions that produce anantimicrobial effect. Other example embodiments, however, are alsocontemplated. For instance, photoactivation devices for deliveringphotoactiving light to corneal tissue are described in U.S. patentapplication Ser. No. 14/248,966, filed Apr. 9, 2014 and titled “Systemsand Methods for Delivering Light in Eye Treatments,” the contents ofwhich are incorporated entirely herein by reference. Suchphotoactivation devices can be modified to include one or more of thefeatures according to aspects of the present disclosure. For example,the devices can be modified to introduce oxygen gas into the environmentof the corneal tissue in a manner similar to the photoactivation device100.

As the outer-most barrier of the cornea, the epithelium functions toregulate nutrients, including oxygen, that are admitted into the stromaltissue from the tear film. This regulation is carried out via theepithelium's physiological “pumps” that are driven by osmotic pressureacross the epithelium due to differential concentrations ofbarrier-permeable solutes on either side of the epithelium. Whenhealthy, certain nutrients in the tear film that become depleted withinthe stroma can permeate the epithelium via osmotic pressure to resupplythe stroma. However, while oxygen and some other small moleculenutrients can reach the stroma according to this mechanism, certainphotosensitizers cannot pass through the epithelium.

Riboflavin, for example, is a relatively large, hydrophilic moleculethat cannot penetrate the tight junctions of the epithelium. Theepithelium slows the amount of riboflavin that can penetrate the stroma.Thus, a variety of approaches have been employed to overcome lowriboflavin diffusivity and deliver sufficient concentrations ofriboflavin to the stroma for performing treatments. For some cornealtreatments, for instance, the epithelium may be removed (epitheliumdebridement) before a riboflavin solution is applied directly to thestroma. Although removing the epithelium allows riboflavin to reach thestroma, the approach is associated with patient discomfort, risks ofinfection, and other possible complications. Furthermore, removing theepithelium may be less appropriate for treatments such as antimicrobialtreatments.

Meanwhile, other approaches avoid epithelial debridement. For instance,riboflavin may be provided in a transepithelial formulation that allowsriboflavin to pass through the epithelium. In particular, sometransepithelial formulations include agents, such as benzalkoniumchloride (BAC), with a specific osmolarity of sodium chloride (NaCl).Formulations including BAC are described, for example, in U.S PatentApplication Publication No. 2010/0286156, filed on May 6, 2009, and U.S.Patent Application Publication No. 2013/0267528, filed on Jan. 4, 2013,the contents of these applications being incorporated entirely herein byreference. Other transepithelial formulations may employ otheradditives, such as ethylenediaminetetraacetic acid (EDTA) ortris(hydroxymethyl)aminomethane (Tris).

Yet other transepithelial formulations may employ non-ionic permeabilityenhancers. Aspects of using transepithelial formulations with suchnon-ionic agents are further described further in U.S. ProvisionalPatent Application No. 62/195,144, filed Jul. 21, 2015, U.S. ProvisionalPatent Application No. 62/255,452, filed Nov. 14, 2015, U.S. ProvisionalPatent Application No. 62/262,919, filed Dec. 4, 2015, and U.S.Provisional patent Application No. 62/263,598, filed Dec. 4, 2015, thecontents of these applications being incorporated entirely herein byreference.

For instance, such transepithelial formulations employ a non-ionic agentthat is chosen using the Hydrophile-Lipophile Balance (HLB) system. TheHLB of a permeability enhancer indicates the balance of hydrophilic andlipophilic groups in the molecular structure of the enhancer.Permeability enhancers (or emulsifiers) for the epithelium include amolecule which has both hydrophilic and lipophilic groups. Moleculeswith HLB number below 9 are considered lipophilic and those above 11 ashydrophilic. Molecules with HLB number between 9 and 11 areintermediate.

For the corneal epithelium, a HLB number that is too great or too smalldoes not help the passage of a photosensitizer through the epithelium. Aspecific HLB range enhances movement of a photosensitizer through theepithelium. Thus, aspects of the present disclosure employ non-ionicagents that have a hydrophilic/lipophilic balance to achieve optimizeddiffusivity through the epithelium and the stroma. Advantageously,non-ionic agents are also less corrosive and damaging to the epitheliumthan ionic agents, such as BAC.

For riboflavin, the HLB range for more effective permeability enhancershas been experimentally determined by the inventors to be betweenapproximately 12.6 and approximately 14.6. A class of permeabilityenhancers includes various forms of polyethylene glycol (PEG) withdifferent aliphatic chain lengths. According to example embodiments,some riboflavin formulations include specific concentrations ofPolidocanol (Polyoxyethylene (9) lauryl ether), which has a HLB numberof approximately 13.6.

Some microbes, such as fungi, have dormant phases, while other microbes,such as Acanthamoeba, can create cystic cell membrane barriers.Advantageously, additives that enhance permeability can increasepenetration and uptake of photosensitizer by microbes and enhance theantimicrobial effect of the photosensitizer.

Additionally or alternatively, another solution and/or mechanical forcesmay be applied to enhance the permeability of the epithelium and allowthe riboflavin to pass more easily through the epithelium. Examples ofapproaches for enhancing or otherwise controlling the delivery of aphotosensitizer to the underlying regions of the cornea are described,for example, in U.S. Patent Application Publication No. 2011/0288466,filed Apr. 13, 2011, and U.S. Patent Application Publication No.2012/0289886, filed May 18, 2012, the contents of these applicationsbeing incorporated entirely herein by reference.

When photosensitizers (e.g., riboflavin) are applied to the cornea, thesubsequent application of photoactivating light (e.g., UVA light) mayresult in cross-linking activity. In particular, the resulting ROSand/or other radicals further interact with the collagen fibrils toinduce covalent bonds that bind together amino acids of the collagenfibrils, thereby cross-linking the fibrils. Such cross-linking activitymay be desired for treatments that modify biomechanical properties ofthe cornea, for instance. For antimicrobial treatments, however, it maybe more preferable to generate minimal cross-linking activity whileproviding the deepest and more predictable generation of ROS for theirantimicrobial effect.

Example embodiments may employ the transepithelial formulationsdescribed above to deliver a photosensitizer through the epithelium andto desired depths in the corneal tissue. The example embodiments caninduce an antimicrobial effect at these depths without inducingcross-linking activity by delivering low doses of photoactivating lightthat can nevertheless reach these depths and sufficiently generate ROS.In other words, the low doses of photoactivating light minimizecross-linking activity but induce the desired antimicrobial effect. Forinstance, some implementations may apply UVA light at an irradiance ofapproximately 0.3 mW/cm² over an extended amount of time to cornealtissue that has been treated with a transepithelial riboflavinformulation with a non-ionic permeability enhancer, such as Polidocanol.

The presence of microbes can be modeled with a molar concentrator, andthe killing efficiency can be represented by the concentration ofmicrobes multiplied by a susceptibility constant for each type ofmicrobe. Additionally, for riboflavin, a model based on thephotochemical kinetic reactions described herein may be modified toinclude an additional molar concentration of microbes. In this manner,the killing efficiency can be calculated and validated by experiment.The total number of photoreactive sites in molar concentration is thesum of two concentrations, microbe molar concentration pluscross-linking site concentration.

By applying a low dose of photoactivating light over an extended amountof time, ROS are generated at desired depths and at rates that allow thewhole thickness of the cornea to reach the killing threshold at oncewhile minimizing cross-linking of the anterior cornea.

FIGS. 2 and 3 illustrate respective graphs of concentrations for ROS andcross-links generated when various doses of UVA light are applied tocorneas treated with a transepithelial riboflavin formulation with anon-ionic permeability enhancer as described above. In particular, thedoses of UVA light are applied at irradiances of 0.1 mW/cm², 0.2 mW/cm²,0.3 mW/cm², 0.4 mW/cm², 0.5 mW/cm², 0.6 mW/cm², 0.7 mW/cm², and 0.8mW/cm² for 10 minutes. As shown in FIGS. 2 and 3, for instance, theresults from an irradiance of 0.3 mW/cm² are predominately dictated byBeer's law and full oxygen depletion is never achieved for the fullstromal thickness as seen with the greater doses. The ROS concentrationprofile as a function of depth is maintained with the irradiance of 0.3mW/cm² but increases with the greater irradiances. Therefore, anantimicrobial threshold can be achieved to a given depth for a givenconcentration of microbes.

FIG. 4 illustrates another photoactivation device 200 that is configuredto activate a photosensitizer, such as riboflavin, that has been appliedto eye tissue according to an antimicrobial treatment. As describedabove, when photoactivated, the photosensitizer generates ROS thatprovides an antimicrobial effect. The eye tissue may be treated with atransepithelial formulation with a non-ionic permeability enhancer asdescribed above.

According to one implementation, a medical practitioner, e.g., a nurse,or the patient (once instructed) places drops of the transepithelialphotosensitizer formulation every 30 to 60 seconds for a period ofapproximately 15 to 20 minutes. The transepithelial photosensitizerformulation can be applied to the eyes without the use of specula.

As shown in FIG. 4, the photoactivation device 200 includes a body 202.The body 202 may be shaped and worn like an eyeglasses frame. As such,the body 202 includes rims 202 a defining openings 202 b allowing thesubject can see through the body 202. The body 202 also includes temples202 c and nosepads 202 d that can support the body 202 on the head ofthe subject. Although the photoactivation device 200 in FIG. 4 resemblesa pair of eyeglasses, it is understood that other shapes andconfigurations may be employed to situate the photoactivation device 200stably about the eyes.

The body 202 includes a plurality of photoactivating light sources 204that can direct photoactivating light to each eye of the subject fromthe top, bottom, left, and right. In some cases, the photoactivatinglight sources 204 may include light-emitting diodes (LED's) that directUVA light simultaneously to eyes that have been treated with ariboflavin formulation. The number of photoactivating light sources 204may be limited to the number required to provide the desired low dose ofphotoactivating light, e.g., delivered at an irradiance of approximately0.3 mW/cm² for approximately at least 10 minutes.

The body 202 also includes a plurality of guide light sources 206 thatemit visible light from above, below, left, and right of each eye. Insome cases, the guide light sources 206 may include LEDs. At least onetop guide light source 206(a) emits light from above each eye; at leastone bottom guide light source 206(b) emits light from below each eye; atleast one left guide light source 206(c) emits light from the left ofeach eye; and at least one right guide light source 206(d) emits lightfrom the right of each eye.

A controller 208, e.g., in the form of an electronic/electricchip/circuit, is coupled to the guide light sources 206. The controller208 can alternately illuminate the guide light sources 206. Inparticular, the controller 208 may repeatedly, in series: (1) illuminatethe top guide light source(s) 206(a) for a predetermined period of time(e.g., 10 seconds or other optimal period) while the other guide lightsources 206(b), (c), (d) remain off; (2) illuminate the bottom guidelight source(s) 206(b) for the predetermined period of time while theother guide light sources 206(a), (c), (d) remain off; (3) illuminatethe left guide light source(s) 206(c) for the predetermined period oftime while the other guide light sources 206(a), (b), (d) remain off;and (4) illuminate the right guide light source(s) 206(d) for thepredetermined period of time while the other guide light sources 206(a),(b), (c) remain off.

FIG. 5 illustrates a method 500 that corresponds to the example above.In step 502, the one or more eyes receive drops of transepithelialphotosensitizer formulation periodically over a specified amount oftime. In step 504, the photoactivation device 200 is placed over the oneor more eyes. In step 506, the one or more eyes look at the guide lightsources 206(a) illuminated at the top of the photoactivation device 200to expose a first area of the one or more eyes to photoactivation lightfrom photoactivating light sources 204 on the photoactivation device200. In step 508, the one or more eyes look at the guide light sources206(b) illuminated at the bottom of the photoactivation device 200 toexpose the one or more eyes to the photoactivation light. In step 510,the one or more eyes look at the guide light sources 206(c) illuminatedat the left of the photoactivation device 200 to expose a third area ofthe one or more eyes to the photoactivation light. In step 512, the oneor more eyes look at the guide light sources 206(d) illuminated at theright of the photoactivation device 200 to expose a fourth area of theone or more eyes to the photoactivation light. In alternativeembodiments, the guide light sources 206 may be alternately illuminatedin a different sequence. Moreover, the guide light sources 206 maydirect light to the eyes from additional directions, e.g., top-left,top-right, bottom-left, bottom-right, etc.

Accordingly, the patient is directed to move his or her eyes to followthe alternately illuminated guide light sources 206 (i.e., up, down, tothe left, to the right, and so on), thereby moving different areas ofthe eye, e.g., corneal surface, to the open area between the top andbottom eyelids. Even with blinking, substantially the entire surface ofeach eye is exposed between the top and bottom eyelids to thephotoactivating light from the photoactivating light sources 204, andthe photosensitizer in the treated tissue can be photoactivated for theantimicrobial effect. In this way, substantially the entire eye surfacegets full coverage of irradiance without the need for specula to forcethe eyes wide open for the delivery of photoactivating light. Thepatient may sit up or lay down for the procedure for as long asnecessary. Because the irradiance is low and the procedure lasts for anextended amount of time, irradiance variation is averaged and greatlyminimized over time.

The body 202 also includes a battery 210 to power the photoactivatinglight sources 204, the guide light sources 206, and the controller 208.Initially, a plastic pull-tab can electrically separate the battery 210from the other components. When the photoactivation device 200 is neededto deliver photoactivating light to the treated eyes, the pull-tab canbe removed to connect the battery 210 with a conductive contact whichdelivers electrical power to the other components. Alternatively, theframe 202 may include an electrical switch that can be selectivelyoperated to connect the battery 210 with the other components. The powerfrom the battery 210 may be limited to what is necessary to operate thephotoactivating light sources 204 and the guide light sources 206 todeliver the photoactivating light to the entire ocular surface with thedesired low irradiance and desired extended irradiation time.

The end of the treatment may coincide with the depletion of power fromthe battery 210. Alternatively, the controller 208 may control theirradiation time. Alternatively, the components of the photoactivationdevice 200 may turn off (e.g., burn out) and self-destruct after a givenamount of irradiation time.

Due to the configuration above, the photoactivation device 200 may beemployed as a single-use, disposable device. The photoactivation device200 does not include any lenses and can be inexpensively manufactured.For instance, the body 202 may be molded from plastic. Becausephotoactivation device 200 is not positioned too close to the eyes(e.g., the surgical field), the photoactivation device 200 should beclean but does not necessarily have to be sterile. Furthermore, thephotoactivation device 200 might not be considered medical waste and assuch may not require special disposal procedures.

The photoactivation device 200 may be configured to become inoperableonce the treatment is complete. For instance, the battery 210 cannot bereplaced once the power is depleted and the treatment is complete.Additionally or alternatively, as described above, the components of thephotoactivation device 200 may self-destruct after a given amount ofirradiation time.

In general, the photoactivation device 200 is more convenient andcost-effective than other irradiation systems. As such, thephotoactivation device 200 may be more feasible for treatments in thethird world and/or other remote locations.

The use of the photoactivation device 200 is not limited to humans.Indeed, the photoactivation device 200 can be especiallymodified/configured for treatment of animals, such as dogs, cats,horses, etc.

As described above, photochemical kinetic reactions can produceantimicrobial agents that place microbes in the tissue under stress andinduce an apoptotic or necrotic response in the microbes. A descriptionof photochemical kinetic reactions for riboflavin is provided, forexample, in International Patent Application No. PCT/US15/57628, filedOct. 27, 2015, the contents of which are incorporated entirely herein byreference. When riboflavin absorbs radiant energy, especially UVA light,it undergoes photoactivation. There are two photochemical kineticpathways for riboflavin photoactivation, Type I and Type II. Some of thereactions involved in both the Type I and Type II mechanisms are asfollows:

Common reactions: Rf → Rf₁*, I; (r1) Rf₁* → Rf, κ1; (r2) Rf₁* → Rf₃* κ2;(r3) Type I reactions: Rf₃* + DH → RfH⁻ + D⁻, κ3; (r4) 2RfH → Rf + RfH₂,κ4; (r5) Type II reactions: Rf₃* + O₂ → Rf + O₂ ¹, κ5; (r6) DH + O₂ ¹ →D_(ox), κ6; (r7) D_(ox) + DH → D − D, κ7; CXL (r8)

In the reactions described herein, Rf represents riboflavin in theground state. Rf*₁ represents riboflavin in the excited singlet state.Rf*₃ represents riboflavin in a triplet excited state. Rf.⁻ is thereduced radical anion form of riboflavin. RfH. is the radical form ofriboflavin. RfH₂ is the reduced form of riboflavin. DH is the substrate.DH.⁺ is the intermediate radical cation. D. is the radical. D_(ox) isthe oxidized form of the substrate.

Riboflavin is excited into its triplet excited state Rf^(*) ₃ as shownin reactions (r1) to (r3). From the triplet excited state Rf^(*) ₃, theriboflavin reacts further, generally according to Type I or Type IImechanisms. In the Type I mechanism, the substrate reacts with theexcited state riboflavin to generate radicals or radical ions,respectively, by hydrogen atoms or electron transfer. In Type IImechanism, the excited state riboflavin reacts with oxygen to formsinglet molecular oxygen. The singlet molecular oxygen then acts ontissue to produce additional cross-linked bonds.

Oxygen concentration in the cornea is modulated by UVA irradiance andtemperature and quickly decreases at the beginning of UVA exposure.Utilizing pulsed light of a specific duty cycle, frequency, andirradiance, input from both Type I and Type II photochemical kineticmechanisms can be employed to achieve a greater amount of photochemicalefficiency. Moreover, utilizing pulsed light allows regulating the rateof reactions involving riboflavin. The rate of reactions may either beincreased or decreased, as needed, by regulating, one of the parameterssuch as the irradiance, the dose, the on/off duty cycle, riboflavinconcentration, soak time, and others. Moreover, additional ingredientsthat affect the reaction and cross-linking rates may be added to thecornea.

If UVA radiation is stopped shortly after oxygen depletion, oxygenconcentrations start to increase (replenish). Excess oxygen may bedetrimental in the corneal cross-linking process because oxygen is ableto inhibit free radical photopolymerization reactions by interactingwith radical species to form chain-terminating peroxide molecules. Thepulse rate, irradiance, dose, and other parameters can be adjusted toachieve a more optimal oxygen regeneration rate. Calculating andadjusting the oxygen regeneration rate is another example of adjustingthe reaction parameters to achieve a desired amount of cornealstiffening.

Oxygen content may be depleted throughout the cornea, by variouschemical reactions, except for the very thin corneal layer where oxygendiffusion is able to keep up with the kinetics of the reactions. Thisdiffusion-controlled zone will gradually move deeper into the cornea asthe reaction ability of the substrate to uptake oxygen decreases.

Riboflavin is reduced (deactivated) reversibly or irreversibly and/orphoto-degraded to a greater extent as irradiance increases. Photonoptimization can be achieved by allowing reduced riboflavin to return toground state riboflavin in Type I reactions. The rate of return ofreduced riboflavin to ground state in Type I reactions is determined bya number of factors. These factors include, but are not limited to,on/off duty cycle of pulsed light treatment, pulse rate frequency,irradiance, and dose. Moreover, the riboflavin concentration, soak time,and addition of other agents, including oxidizers, affect the rate ofoxygen uptake. These and other parameters, including duty cycle, pulserate frequency, irradiance, and dose can be selected to achieve moreoptimal photon efficiency and make efficient use of both Type I as wellas Type II photochemical kinetic mechanisms for riboflavinphotosensitization. Moreover, these parameters can be selected in such away as to achieve a more optimal chemical amplification effect.

In addition to the photochemical kinetic reactions (r1)-(r8) above,however, the present inventors have identified the followingphotochemical kinetic reactions (r9)-(r26) that also occur duringriboflavin photoactivation:

Rf₃* → Rf, κ8; (r9) Rf₃* + Rf → 2RfH^(•), κ9; (r10) RfH₂ + O₂ →RfH^(•) + H⁺ + O₂ ⁻, κ10; (r11) RfH^(•) + O₂ → Rf + H⁺ + O₂ ⁻, κ11;(r12) 2RfH₂ + O₂ ⁻ → 2RfH^(•) + H₂O₂, κ12; (r13) 2RfH^(•) + O₂ ⁻ → 2Rf +H₂O₂, κ13; (r14) RfH^(•) + H₂O₂ → OH^(•) + Rf + H₂O, κ14; (r15) OH^(•) +DH → D^(•) + H₂O, κ15; (r16) D^(•) + D^(•) → D − D, κ16; CXL (r17) O½ →O₂, κ18; (r18) D^(•) + RfH₂ → RfH^(•) + DH, κ19; (r19)

κ_(a) = κ_(a) ⁺/κ_(a) ⁻ (r20)

κ_(a) = κ_(a) ⁺/κ_(a) ⁻ (r21)

κ_(b) = κ_(b) ⁺/κ_(b) ⁻ (r22) Rf₁* + A → Rf + A, κ_(1a) (r23) Rf₃* + A →Rf + A, κ_(3a) (r24) 2O₂ ⁻ → H₂O₂ κ₁₂ (r25) OH* + CXL → inert products,κ_(OH) (r26)

FIG. 6 illustrates a diagram for the photochemical kinetic reactionsprovided in reactions (r1) through (r26) above. The diagram summarizesphotochemical transformations of riboflavin (Rf) under UVAphotoactivating light and its interactions with various donors (DH) viaelectron transfer. As shown, cross-linking activity occurs: (A) throughthe presence of singlet oxygen in reactions (r6) through (r8) (Type IImechanism); (B) without using oxygen in reactions (r4) and (r17) (Type Imechanism); and (C) through the presence of peroxide (H₂O₂), superoxide(O₂.), and hydroxyl radicals OH) in reactions (r13) through (r17).

As shown in FIG. 6, the present inventors have also determined that thecross-linking activity is generated to a greater degree from reactionsinvolving peroxide, superoxide, and hydroxyl radicals. Cross-linkingactivity is generated to a lesser degree from reactions involvingsinglet oxygen and from non-oxygen reactions. Some models based on thereactions (r1)-(r26) may account for the level of cross-linking activitygenerated by the respective reactions. For instance, where singletoxygen plays a smaller role in generating cross-linking activity, modelsmay be simplified by treating the cross-linking activity resulting fromsinglet oxygen as a constant.

All the reactions start from Rf₃* as provided in reactions (r1)-(r3).The quenching of Rf₃* occurs through chemical reaction with ground stateRf in reaction (r10), and through deactivation by the interaction withwater in reaction (r9).

Excess oxygen may be detrimental in corneal cross-linking process. Asshown in FIG. 6, when the system becomes photon-limited andoxygen-abundant, cross-links can be broken from further reactionsinvolving superoxide, peroxide, and hydroxyl radicals. Indeed, in somecases, excess oxygen may result in net destruction of cross-links versusgeneration of cross-links.

A large variety of factors as described herein affect the rate of thecross-linking reaction and the amount of biomechanical stiffnessachieved due to cross-linking. A number of these factors areinterrelated, such that changing one factor may have an unexpectedeffect on another factor. However, a more comprehensive model forunderstanding the relationship between different factors for riboflavintreatment is provided by the photochemical kinetic reactions (r1)-(r26)identified above. Accordingly, systems and methods can adjust variousparameters for photosensitizer treatment according to this photochemicalkinetic model, which provides a unified description of oxygen dynamicsand cross-linking activity. The model can be employed to evaluateexpected outcomes based on different combinations of treatmentparameters and to identify the combination of treatment parameters thatprovides the desired result. The parameters, for example, may include,but is not limited to: the concentration(s) and/or soak times of theapplied photosensitizer; the dose(s), wavelength(s), irradiance(s),duration(s), and/or on/off duty cycle(s) of the photoactivating light;the oxygenation conditions in the tissue; and/or presence of additionalagents and solutions.

As further described above, example embodiments can generate ROS atdesired depths and at rates to achieve an antimicrobial effectthroughout the thickness of the cornea while minimizing cross-linking ofthe anterior cornea. The photochemical kinetic reactions above can beemployed to determine the threshold at which cross-linking activity isgenerated at depths within the cornea. Using a model based on thephotochemical kinetic reactions, the example embodiments can beconfigured accordingly to generate ROS for the antimicrobial effectwithout reaching the determined threshold for cross-linking activity.

It is understood, however, that alternative embodiments may call forcross-linking activity (to modify biomechanical properties) in additionto antimicrobial treatment. As such, the model based on thephotochemical kinetic reactions allows these alternative embodiments togenerate ROS and/or other radicals for the desired antimicrobial effectand desired cross-linking activity.

In addition to the factors described above, example embodiments mayenhance the photochemical kinetic reactions by adding a metal, such asiron or copper, to the riboflavin formulation. A description of howadditives can affect photochemical kinetic reactions is provided, forexample, in U.S. patent application Ser. No. 14/281,638, filed May 19,2014 and titled “Systems, Methods, and Compositions for Cross-Linking”and U.S. Provisional Patent Application No. 62/086,572, filed Dec. 2,2014 and also titled “Systems, Methods, and Compositions forCross-Linking,” the contents of these application being incorporatedentirely herein by reference.

For instance, trace amounts of copper (ranging from approximately 0.1 mMto approximately 10 mM) can provide an enhanced antimicrobial effect fora riboflavin formulation. Copper can enhance the photodynamic effect ofriboflavin through a Fenton-type reaction. Moreover, copper on its own(specifically, copper ions) can have an antimicrobial effect even whenit is not combined with a photosensitizer. Therefore, the enhanced modeof action for a riboflavin formulation with a copper additive involvesenhancement though the Fenton-type reaction and/or the antimicrobialeffect of the copper by itself.

The photochemical kinetic reactions for a riboflavin formulation can beenhanced by adding a deuterated water (D₂O), also known as “heavywater.” D₂O by itself does not kill bacteria. Skladnev D. A., et al.Methylotrophic Bacteria as Sources of 2H- and 13C-amino Acids.Biotechnology (1996), pp. 14-22. However, D₂O can increase the presenceof singlet oxygen when used in combination with a photosensitizerformulation (and optionally other additives). Singlet oxygen is one ofthe ROS responsible for producing an antimicrobial effect through TypeII photochemical kinetic energy transfer. Type II photochemical kineticreactions are described, for example, in U.S. patent application Ser.No. 13/841,617 cited above. Thus, example embodiments may employ D₂O toenhance the antimicrobial effect associated with singlet oxygen.

Example embodiments may also employ timed application of agents, such asdimethyl sulfoxide (DMSO), which can cause penetration of aphotosensitizer to desired depths in the targeted tissue and produce anantimicrobial effect at the desired depths. In some cases, theantimicrobial effect at the desired depths may be further enhanced byincreasing the oxygen concentration available for the photochemicalreactions with the photosensitizer.

Example embodiments may also employ timed application of quenchingagents to generate greater antimicrobial effect at the desired depths.The quenching agents can limit the photochemical reaction in regionscloser to the surface of the tissue and allow the antimicrobial effectof the photosensitizer to take place deeper in the tissue. Quenchingagents are described, for example, in U.S. patent application Ser. No.13/475,175, filed May 18, 2012 and titled “Controlled Application ofCross-Linking Agent,” the contents of which are incorporated entirelyherein by reference.

Example embodiments may also increase or decrease the pH of the tissueto enhance the antimicrobial effect of antimicrobial treatments. The pHof the tissue may be modified by selectively applying acidic or basicsolutions. In some cases, the acidic or basic solutions may includeadditives as described herein. For example, the solutions may includequenching agents to control the photochemical reactions at a given depthwithin the tissue.

Example embodiments may employ a dispensing device configured to applydifferent formulations and/or different concentrations according to apredetermined sequence. The dispensing device, for instance, may be acharged nanocloud device that applies the photosensitizer formulationsvia aerosolized electro-spraying. In some cases, the dispensing devicemay generate and deliver a dual payload of ionized ROS encapsulated inphotosensitizer nanoparticles for simultaneous intra-stromal deposition.

Example embodiments may additionally employ water nanoparticles forantimicrobial applications. Electro-spraying ionized water (“engineeredwater”) results in nano-caging ROS via an excess of electrons loadedduring droplet fission thereby conferring the nanoparticles withantimicrobial properties.

Example embodiments may employ nanostructures to promote delivery ofphotosensitizer formulations to the target tissue and enhance theantimicrobial effect of the photochemical kinetic reactions. Thenanostructures may include, but are not limited to, liposomes, polymericmicelles, ceramic (graphene oxide) and metallic nanorods. Thesenanostructures may be included in drops that are applied to the targettissue. Alternatively, specially configured structures may be employedto allow the nanostructures and photosensitizer formulations topenetrate the target tissue.

For instance, a contact lens device may be configured to allow differentphotosensitizer formulations and nanostructures to penetrate a cornea ina corneal procedure. The contact lens device may be applied to thecornea for several minutes or even a few hours before illumination isapplied to initiate photochemical kinetic reactions. Such a devicefacilitates delivery through the epithelium for procedures that keep theepithelium in place, i.e., “epi-on” procedures.

In an example procedure, very low concentrations of drug formulation maybe applied to eye tissue, followed by application of illumination atvery low irradiance levels, e.g., a formulation with approximately 0.02%riboflavin concentration followed by approximately 1 mW/cm² illuminationof UV light. The contact lens devices described above can be applied tothe subject's eyes for 30-90 minutes to deliver the formulation. Oncethe contact lens devices are removed and the photoactivation device 100is positioned over the subject's eyes to deliver the illumination togenerate the photochemical kinetic reactions.

In view of the foregoing, example embodiments can enhance antimicrobialtreatments by any combination of:

-   -   employing different photosensitizer formulations at various        concentrations;    -   employing specialized additives with the photosensitizer        formulation(s);    -   controlling oxygen available to the photochemical reactions        through hyperbaric, hyperoxic, and/or hypoxic conditions;    -   employing time dependent quenching agents;    -   manipulating temperature of the target tissue;    -   manipulating the pH of the photosensitizers or additives;    -   employing nanostructures;    -   controlling the delivery of photosensitizer(s) to the tissue;        and/or    -   controlling the delivery of light to the target tissue treated        with the photosensitizer formulation(s).

Although the example embodiments above involve treatments of the eye, itis understood that aspects of the present disclosure can be applied totreatments of other parts of the body. For instance, alternativeapplications such as Ventilator Associated Pneumonia (VAP) treatmentscan be addressed by the use of combinations of aerosolizeddrugs/photosensitizers and ionized ROS in water nanoparticles. These canbe delivered to the oral and tracheal regions with targeted multi-drugresistant anti-bacterial payloads (MDR A. baumannii, P. aeruginosa). Inan example VAP application, a pre-tracheal mouthpiece tube havingactinic illumination targets ROS-photosensitizer nanoparticles flowinginto the oral cavity.

The embodiments described herein may employ controllers and otherdevices for processing information and controlling aspects of theexample systems. For example, the example photoactivation device 100shown in FIGS. 1a, b includes the controller 116 or the photoactivationdevice 200 shown in FIG. 4 includes the controller 208. Generally, thecontrollers include one or more processors. The processor(s) of acontroller or other devices may be implemented as a combination ofhardware and software elements. The hardware elements may includecombinations of operatively coupled hardware components, includingmicroprocessors, memory, signal filters, electronic/electricchip/circuit, etc. The processors may be configured to performoperations specified by the software elements, e.g., computer-executablecode stored on computer readable medium. The processors may beimplemented in any device, system, or subsystem to provide functionalityand operation according to the present disclosure. The processors may beimplemented in any number of physical devices/machines. Indeed, parts ofthe processing of the example embodiments can be distributed over anycombination of processors for better performance, reliability, cost,etc.

The physical devices/machines can be implemented by the preparation ofintegrated circuits or by interconnecting an appropriate network ofconventional component circuits, as is appreciated by those skilled inthe electrical art(s). The physical devices/machines, for example, mayinclude field programmable gate arrays (FPGA's), application-specificintegrated circuits (ASIC's), digital signal processors (DSP's), etc.

Appropriate software can be readily prepared by programmers of ordinaryskill based on the teachings of the example embodiments, as isappreciated by those skilled in the software arts. Thus, the exampleembodiments are not limited to any specific combination of hardwarecircuitry and/or software. Stored on one computer readable medium or acombination of computer readable media, the computing systems mayinclude software for controlling the devices and subsystems of theexample embodiments, for driving the devices and subsystems of theexample embodiments, for enabling the devices and subsystems of theexample embodiments to interact with a human user (user interfaces,displays, controls), etc. Such software can include, but is not limitedto, device drivers, operating systems, development tools, applicationssoftware, etc. A computer readable medium further can include thecomputer program product(s) for performing all or a portion of theprocessing performed by the example embodiments. Computer programproducts employed by the example embodiments can include any suitableinterpretable or executable code mechanism, including but not limited tocomplete executable programs, interpretable programs, scripts, dynamiclink libraries (DLLs), applets, etc. The processors may include, or beotherwise combined with, computer-readable media. Some forms ofcomputer-readable media may include, for example, a hard disk, any othersuitable magnetic medium, any suitable optical medium, RAM, PROM, EPROM,flash memory, any other suitable memory chip or cartridge, any othersuitable non-volatile memory, a carrier wave, or any other suitablemedium from which a computer can read.

The controllers and other devices may also include databases for storingdata. Such databases may be stored on the computer readable mediadescribed above and may organize the data according to any appropriateapproach. For example, the data may be stored in relational databases,navigational databases, flat files, lookup tables, etc.

While the present invention has been described with reference to one ormore particular embodiments, those skilled in the art will recognizethat many changes may be made thereto without departing from the spiritand scope of the present invention. Each of these embodiments andobvious variations thereof is contemplated as falling within the spiritand scope of the invention. It is also contemplated that additionalembodiments according to aspects of the present invention may combineany number of features from any of the embodiments described herein.

What is claimed is:
 1. An antimicrobial treatment system comprising awearable photoactivation device including: a body defining a chambershaped to be positioned over and enclose one or more eyes of a subject,the body including one or more windows that allow the one or more eyesto see through the body; one or more photoactivating light sourcescoupled to the body and configured to direct photoactivating light tothe one or more eyes according to illumination parameters, theillumination parameters determining a dose of the photoactivating lightthat activates, according to photochemical kinetic reactions, aphotosensitizer applied to the one or more eyes and generates reactiveoxygen species that provide an antimicrobial effect in the one or moreeyes; and an inlet configured to couple the body to an oxygen source,the chamber receiving oxygen from the oxygen source via the inlet tomodify oxygen conditions in the chamber, the activation of thephotosensitizer depending on the oxygen conditions.
 2. The antimicrobialtreatment system of claim 1, wherein the one or more photoactivatinglight sources deliver the photoactivating light as at least one ofpulses or continuous wave, and the illumination parameters include atleast one of wavelength, power, irradiance, intensity, duration, or dutycycle.
 3. The antimicrobial treatment system of claim 1, wherein thephotosensitizer includes riboflavin, the one or more photoactivatinglight sources deliver ultraviolet light.
 4. The antimicrobial treatmentsystem of claim 3, wherein the dose of the photoactivating lightactivates the photosensitizer and generates reactive oxygen species thatprovide the antimicrobial effect in the one or more eyes, withoutsubstantially inducing cross-linking activity that producesbiomechanical changes in the one or more eyes.
 5. The antimicrobialtreatment system of claim 1, further comprising a controller includingone or more processors and one or more computer readable media, the oneor more processors configured to execute instructions from the computerreadable media to: determine the illumination parameters based on amodel of the photochemical kinetic reactions; and operate the one ormore photoactivating light sources according to the illuminationparameters.
 6. The antimicrobial treatment system of claim 1, whereinthe photoactivation device further includes one or more heating elementscoupled to the body and configured to generate heat in the chamberaccording to temperature parameters, the temperature parametersmodifying, according to the photochemical kinetic reactions, theactivation of the photosensitizer applied to the one or more eyes andthe generation of reactive oxygen species that provide the antimicrobialeffect in the one or more eyes.
 7. The antimicrobial treatment system ofclaim 6, further comprising a controller including one or moreprocessors and one or more computer readable media, the one or moreprocessors configured to execute instructions from the computer readablemedia to: determine the temperature parameters based on a model of thephotochemical kinetic reactions; and operate the one or more heatingelements according to the temperature parameters.
 8. The antimicrobialtreatment system of claim 1, wherein the oxygen from the oxygen sourcemodifies the temperature in the chamber according to temperatureparameters, the temperature parameters modifying, according to thephotochemical kinetic reactions, the activation of the photosensitizerapplied to the one or more eyes and the generation of reactive oxygenspecies that provide the antimicrobial effect in the one or more eyes.9. The antimicrobial treatment system of claim 8, further comprising acontroller including one or more processors and one or more computerreadable media, the one or more processors configured to executeinstructions from the computer readable media to: determine thetemperature parameters based on a model of the photochemical kineticreactions; and operate the oxygen source according to the temperatureparameters.
 10. A wearable antimicrobial treatment device, comprising: abody shaped to be positioned on a head of a subject over one or moreeyes, the body including one or more openings that allow the one or moreeyes to see through the body; one or more photoactivating light sourcescoupled to the body and configured to direct photoactivating light tothe one or more eyes according to illumination parameters, theillumination parameters determining a dose of the photoactivating lightthat activates, according to photochemical kinetic reactions, aphotosensitizer applied to the one or more eyes and generates reactiveoxygen species that provide an antimicrobial effect in the one or moreeyes; a plurality of guide light sources coupled at a plurality ofpositions about the body and configured to direct visible light to theone or more eyes from a plurality of directions; and a controllerconfigured to operate the guide light sources to alternately direct thevisible light from each direction according to a sequence wherein thesubject is directed to look, with the one or more eyes, in eachdirection according to the sequence and different respective areas ofthe one or more eyes are exposed to the photoactivating light from theone or more photoactivating light sources.
 11. The wearableantimicrobial treatment device of claim 10, wherein the one or morephotoactivating light sources delivers the photoactivating light as atleast one of pulses or continuous wave, and the illumination parametersinclude at least one of wavelength, power, irradiance, intensity,duration, or duty cycle.
 12. The wearable antimicrobial treatment deviceof claim 10, further comprising a battery coupled to the photoactivatinglight sources, wherein the photoactivating light is directed to the oneor more eyes according to a duration determined by a battery life of thebattery.
 13. The wearable antimicrobial treatment device of claim 10,wherein the photosensitizer includes riboflavin, the one or morephotoactivating light sources deliver ultraviolet light.
 14. Thewearable antimicrobial treatment device of claim 10, wherein the dose ofthe photoactivating light activates the photosensitizer and generatesreactive oxygen species that provide the antimicrobial effect in the oneor more eyes, without substantially inducing cross-linking activity thatproduces biomechanical changes in the one or more eyes.
 15. The wearableantimicrobial treatment device of claim 10, wherein the body is shapedas a frame for eyeglasses including one or more rims, temples, andnosepads, the one or more rims defining the one or more openings, andthe temples and nosepads supporting the body on the head of the subject.16. The wearable antimicrobial treatment device of claim 10, wherein thecontroller is further coupled to the one or more photoactivating lightsources and configured to operate the one or more photoactivating lightsources according to the illumination parameters.
 17. An antimicrobialtreatment system, comprising a wearable photoactivation systemincluding: a body configured to be positioned on a head of a subjectover one or more eyes of the subject, the body including one or morewindows or openings that allow the one or more eyes to see through thebody; and one or more photoactivating light sources coupled to the bodyand configured to direct photoactivating light to the one or more eyesaccording to illumination parameters, the illumination parametersdetermining a dose of the photoactivating light that activates,according to photochemical kinetic reactions, a photosensitizer appliedto the one or more eyes and generates reactive oxygen species thatprovide an antimicrobial effect in the one or more eyes, withoutsubstantially inducing cross-linking activity that producesbiomechanical changes in the one or more eyes.
 18. The antimicrobialtreatment system of claim 17, wherein the photosensitizer includes atransepithelial riboflavin formulation that penetrates to a depth in theone or more eyes, the one or more photoactivating light sources emitultraviolet light, and the illumination parameters determine the dose ofthe ultraviolet light that reaches the depth in the one or more eyes.19. The antimicrobial treatment system of claim 18, wherein the one ormore photoactivating light sources emit the ultraviolet light at anirradiance of approximately 0.3 mW/cm².
 20. The antimicrobial treatmentsystem of claim 17, further comprising a controller including one ormore processors and one or more computer readable media, the one or moreprocessors configured to execute instructions from the computer readablemedia to: determine the illumination parameters based on a model of thephotochemical kinetic reactions; and operate the one or morephotoactivating light sources according to the illumination parameters.